Lombardi's opened on Spring Street in 1905 as a grocery licensed to sell tomato pies, cut and wrapped in paper, tied with string, sold by the half to laborers who could not afford a whole one. The New York slice was a ration before it became a meal. No other American city built a food economy around a single wedge sold through a window. That economic logic still governs the city's pizza geography, and it explains why NYC Pizza Walking Tour tours are built around sidewalks rather than coaches. The dough followed the tenements. Neapolitan bakers settling around Mulberry Street worked with coal-fired ovens because coal was what the buildings already burned, and those ovens ran hot enough, above 800°F, to blister a crust in minutes. Fewer than a dozen coal-burning pizza ovens remain licensed in the five boroughs; new ones have been effectively impossible to permit for decades. Gas deck ovens replaced them, running cooler and longer, which is how the foldable, wide-diameter slice became standard. Sicilian bakers contributed the square, the thick-edged pan pie sold by weight in Brooklyn bread shops. Those two formats, round and square, coal and gas, still define nearly every menu between Houston Street and Canal Street. Geography did the rest. Little Italy contracted to roughly three blocks of Mulberry Street as Chinatown expanded north and east, so the two neighbourhoods now share intersections where a pork bun counter sits four doors from a brick-oven parlour. The Lower East Side kept its knish bakeries and pickle counters. Greenwich Village holds the busiest by-the-slice windows in the city. Street grids help: below Houston Street the blocks are short, irregular and pre-grid, a survival of the colonial lanes that the 1811 Commissioners' Plan never reached. On foot, these transitions occur in under fifteen minutes of walking, which is the argument for a New York pizza tour over any vehicle. What visitors encounter is less a cuisine than a record of arrivals. Mozzarella recipes brought from Campania, Sicilian pan technique, Chinese-Italian hybrid bakeries that appeared in the 1980s, and the dollar-slice economy of the 2000s all occupy the same twenty-minute radius. Little Italy food tasting walks and Lower East Side food walking tours trace that layering through ovens, counters and back rooms that rarely advertise. Guides tend to read the ovens as documents: the brick arch, the ash door, the thermometer glued above it. NYC Pizza Walking Tour tickets cover guided routes across these streets, and the ovens remain the clearest surviving evidence of how the city fed itself.